Firewood is used in fire places for heating. Firewood can be made from wood, such as logs, e.g. by using firewood processors. Firewood processors both cut (i.e. saw) and split wood to obtain firewood. A firewood processor is known e.g. from U.S. Pat. No. 4,173,237.
The quality of firewood depends e.g. on its size and the amount of impurities, such as debris, bark, and/or sawdust, intermixed with the firewood. Referring to FIGS. 1a-1c, firewood has usually a length, L, from 15 cm to 100 cm, mainly depending on national tradition and/or the size of the fireplace. Specific examples include 400 mm and 500 mm for typical boilers, and 330 mm and 250 mm for typical fireplaces. In addition, the transversal maximum measure of the firewood, herein called as the width of the firewood, should be reasonably small, depending on the class of the firewood. For example, for the classes “A1, D15”, and “A2, D15” as defined in the standard EN 14961-5, the width of the firewood, D, should be at most 15 cm.
When the diameter of the un-split wood 100 (see FIGS. 2a-2c) is more than 15 cm, a one-way splitting wedge 110, as described in U.S. Pat. No. 4,173,237 and FIG. 2a, cannot be used to produce firewood having small width in one go. A splitting wedge 120 can be arranged to split a log to four parts (See. FIG. 2b), whereby somewhat thicker wood can be split to comply the width requirements for firewood. Theoretically, wood with a diameter of about 21 cm could be cut to sufficiently small firewood with such a splitting wedge. Moreover, theoretically, wood with a diameter of 30 cm could be cut to sufficiently small firewood with e.g. a splitting wedge arranged to split the wood to at least six pieces, the splitting wedge having only radial splitting parts, as the wedge of FIG. 2b. In practice, however, it is hard to align the center of the splitting wedge with the center of the log to be split. Moreover, the grains of a log are not precisely parallel to the length, whereby the log will not split ideally along its central axis. The splitting wedge 120 can be arranged in a frame 122. The size of the frame 122 is selected large enough for the wood 100, so that so that split wood can move radially outwards in the open sections “O” of the splitting wedge, as depicted in FIG. 2b. 
When the diameter of the un-split wood 100 is even larger, such as about 30 cm or more, such a splitting wedge is not able to split the wood to sufficiently small firewood in one go. Naturally, it is possible to manually detect and pick too large pieces of wood, and re-split them with the same wedge. This, however, considerably slows down the process. Furthermore, moving large pieces of wood manually may be problematic from a point of view of safety or ergonomics. Moreover, any splitting wedge, wherein the wedges extend only radially cannot be used for the purpose, since the width of the firewood would always be too large. However, it is known in the art to use a splitting wedge 130 that has also bridging parts 134, i.e. parts that extend in the tangential direction. An example of such a wedge is shown in FIG. 2c. 
The problem with splitting wedges 130 having also bridging parts 134 is that when such a wedge is used, the force required to split the log increases a lot. This is mainly because the central pieces of firewood must move through the central apertures “C” of the splitting wedge 130, and therein the movement of the split firewood is limited also from outwards. In contrast, when using e.g. a four-way wedge, as above, the pieces of firewood may move radially away from the center (see FIG. 2b). It is also noted the radially outmost parts of the splitting wedge 130 of FIG. 2c are open, as denoted by the letter “O”. This applies when a frame 122 that is larger than the log is used to support the blades of the splitting wedge, as depicted in FIG. 2b, because the log 100 is relatively thin compared to the frame 122.
The need for large splitting forces impose other problems: the piston for moving the log towards the splitting wedge must be capable of producing the force, and the frame of the firewood processor must be so sturdy that it withstands the forces. In practice this means larger machine parts and a larger firewood processor, which considerably increases the manufacturing and transportation costs for the firewood processor. Moreover, the operation of the firewood processor may slow down, if the size hydraulic pumps are not increased correspondingly. In addition, larger pumps need more energy.
In addition, the processed firewood should be clean. For the purpose it is known to convey the firewood to a sieving drum before packing the firewood. However, sieving drums are reasonably long, in order to ensure sufficient amount of cleaning. A long sieving drum requires a reasonably amount a material, whereby its manufacturing cost may be reasonably high. Moreover, provided that a conveyor for firewood is needed, the sieving drum should be installed in between such conveyor and the firewood processor, which makes the assembly of such a system more complex than a sieving means that is integrated directly to the firewood processor.